A semi-rigid sheet, and in particular a sheet of corrugated cardboard, is cut in conventional cutting machines by using a cutting tool or "die" and a backing surface or "anvil". The cutting tool comprises blades or edges perpendicular to the backing surface when the sheet is compressed between the backing surface and the cutting tool such that the edges pass through the sheet and make the corresponding cuts.
In a first type of cutting machine, the cutting tool is positioned flat on a tool-carrier plate and the backing surface is a plane surface. Under such circumstances, cutting is performed by pressing the backing surface against the tool-carrier plate on which the sheet to be cut has been positioned. The pressure that needs to be used in a cutting machine of that type is very high, sometimes being as great as several thousands of kilonewtons.
In a second type of cutting machine, the cutting tool is mounted on the periphery of a cylinder and the backing surface is itself a cylindrical surface. Cutting is performed by inserting the sheet between the two cylinders that are driven in rotation. The pressure used is much smaller since cutting takes place linearly along the line of tangential contact or "nip" between the two cylinders. However, it is very difficult to shape a cutting tool so that it can be fitted on the outside surface of a cylinder. In addition, problems can arise when the sheet to be cut is quite thick because the cutting edges are mounted radially, so there is a difference in the peripheral distance between the top portions and the bottom portions of two adjacent cutting edges.
In a third type of cutting machine, as disclosed, for example, in document U.S. Pat. No. 3,765,286, the cutting tool is mounted on a tool-carrier plate end the backing surface is a cylindrical surface. That particular disposition makes it possible to mitigate the drawbacks of the first two types. Nevertheless, in that case, the tool-carrier plate must be driven with reciprocating forward-and-return motion enabling each sheet to be displaced one after the other beneath or over the backing cylinder from a sheet feed position to a position for removing the cut sheet. In addition, given that the sheet to be cut comes from an earlier station, either a printing machine or a feeder, the culling machine also includes its own feed means enabling said sheet in particular to be placed accurately on the cutting tool during displacement thereof beneath the backing cylinder. It is necessary firstly for the sheet to be very accurately positioned on the cutting tool, and secondly for it to be impossible for any slip of the sheet to occur as it goes under the backing cylinder. In document FR 2 257 573, the feed means are constituted by two sheet transport systems. The first system, referred to as a "transfer belt" receives the sheet from the upstream machine, which may be a feeder or a printer, for example. It has constant linear speed equal to the speed of said machine. The second machine, referred to as a "launching belt" receives the sheet from the transfer belt and inserts it between the tool-carrier plate and the backing cylinder. Its initial speed is therefore equal to that of the transfer belt, after which it accelerates the sheet so as to give it a speed that is equal to that of the backing cylinder while applying thereto the same acceleration relationship as that which applies to the tool-carrier plate.
In cutting machines of the third type, the backing cylinder includes a covering that is made either of steel or else of a flexible material such as polyurethane. Which one of those coverings is used depends on the quality of cutting that it is desired to obtain. A cleaner cut is obtained when the covering is made of steel, but this causes the cutting edges to wear much more quickly. Such wear can rapidly cause so-called "angel hairs" to be formed, i.e. strips that are very narrow, e.g. about one-tenth of a millimeter wide, and that correspond to the sheet being crushed by a worn cutting blade. The use of a backing cylinder having a steel covering also requires positioning of the cylinder to be adjusted very accurately relative to the tool-carrier plate.
The use of a covering made of flexible material on the backing cylinder makes it possible to avoid "angel hairs" and to avoid the need for accurate adjustment. However, cutting is of poorer quality and cut edges are less clean because of the relative penetration of the cutting edges into the covering of the backing cylinder.
In conventional installations, the quality of cut is a function of the type of cylinder with which the cutting machine is fitted. The user therefore has no way of selecting quality of cut as a function of a particular batch to be treated.